It seems that serological absorption by lyophilized malignant tissue is an accurate screening procedure to detect adenocarcinoma in which antigens (A or P1) appear in violation of all laws of heredity. This procedure will be routinely applied to determine the frequency of adenocarcinomas of stomach, uterus, colon and other organs to determine the frequency of the appearance of neo-A antigen in group O or B patients. The pp yields P1 mutation is a very rare event. The anti-A titer in groups O or B patients suspected of harboring a solid tumor can then be monitored. A very low titer may indicate in vivo specific absorption. In the event of post operative histologic confirmation, attempts to increase the patient's anti-A can then be attempted by intravenous injection of minute quantities of incompatible group A blood. The hope is to maintain the high titer and thus prevent post-operative metastases by cytotoxicity. Will the high titer of anti-A cytotoxicity suffice to destroy the malignancy in the absence of surgery? This can be put to the test by finding a satisfactory animal model, such as the dog. Its tissue occasionally becomes malignant and distinct normal blood group differences exist. Such a study is underway in cooperation with Dr. William Hardy. The gaining of an antigen adds a new dimension to our outlook on mutations inducing malignancy other than the concept of derepression and fetal antigens. It is the addition or substitution of an A-like chain in the O yields A or B yields A mutation that opens the door to the use of blood group antibodies as potential specific cytotoxic agents directed against the malignant tissue.